A solid polymer fuel cell has a structure in which catalyst layers (electrode layers) are stacked on both surfaces of a polymer electrolyte membrane having proton conductivity. This structure is referred to as a “membrane-electrode assembly (MEA)”. Gas diffusion layers are formed on both surfaces of the membrane-electrode assembly to form a membrane-electrode-gas diffusion layer assembly. The membrane-electrode-gas diffusion layer assembly is hermetically sandwiched between a pair of separators, on each of which a gas passage is formed, to form a cell. The cells are stacked to form a structure called a stack.
An oxidant gas, such as oxygen, is supplied to one surface (cathode side) of the polymer electrolyte membrane through the passage of one of the separators. A fuel, such as hydrogen, is supplied to the other surface (anode side) of the polymer electrolyte membrane through the passage of the other separator. On the anode side, the fuel diffuses in the gas diffusion layer and reaches the catalyst layer. In the catalyst layer, protons and electrons are generated from the fuel by an electrode reaction. The protons pass through the polymer electrolyte membrane and move to the cathode side. On the cathode side, the oxidizing agent diffuses in the gas diffusion layer and reaches the catalyst layer. In the catalyst layer, water, etc. are generated from the protons and the oxidizing agent by the electrode reaction. The electrode reactions on the cathode side and on the anode side are accelerated by a catalyst, such as platinum or the like, included in the catalyst layers. The electrons are also attracted to the cathode side. However, by extracting the flow of the electrons outside, the energy of a chemical reaction (oxidation-reduction reaction) can be utilized as power.
In the case of manufacturing the stack, the polymer electrolyte membrane is sandwiched between the electrodes and the separators, and fastened by end plates and bolts. The polymer electrolyte membrane needs to have an adequate strength so as to endure the fastening pressure and not to be physically damaged by abrasion in a long-period use. In contrast, for the purpose of, for example, improving the proton conductivity, the polymer electrolyte membrane needs to be as thin as possible. For the reasons above, it is desirable to increase the strength of the polymer electrolyte membrane without increasing the thickness.
As a technique for solving the above problems, there is the solid polymer fuel cell disclosed in Experimental Example 2 of Patent Document 1. In the solid polymer fuel cell, the strength of the polymer electrolyte membrane is improved by attaching a frame to a peripheral portion of the polymer electrolyte membrane. The catalyst layer is applied on carbon nonwoven fabric (gas diffusion layer), and is joined to the polymer electrolyte membrane to which the frame is attached. The carbon nonwoven fabric (gas diffusion layer) and the catalyst layer are joined to the polymer electrolyte membrane so as to be formed to be slightly (about 1 mm) larger than a hole of the frame on both sides of the hole such that the catalyst layer completely covers the inside of the frame.
Patent Document 1: Japanese Unexamined Patent Application Publication 10-308228